1. Field of the Invention
The present invention relates to a power apparatus which attaches or detaches a battery unit to or from the main body of a cellular phone and an electronic equipment using a power apparatus. Specifically, the present invention relates to a power apparatus which supplies electric power by switching, for example, a second battery connected externally to a cellular phone and a first battery disposed inside the main body of the cellular phone, and an electronic equipment using a power apparatus.
2. Description of the Related Art
Since portable electronic equipments such as cellular phones use batteries as the power apparatus, the cellular phones become unusable when the remaining battery level runs out. Therefore, some types of cellular phones have been proposed, wherein a plurality of batteries are provided and the battery voltage is monitored so as to give out an alarm (warning message) when the remaining battery level is running low (see Patent Literature 1 that is Japanese Patent Laid-Open No. 2000-165514).
A user who noticed the above-mentioned warning message, for example, had to stop using the cellular phone and change or charge the battery. In addition, other types of cellular phones have been proposed, wherein a built-in battery and an external battery are provided so as to switch between each other when either of the remaining battery level runs out, thereby keeping the cellular phone operating (see Patent Literature 2 that is Japanese Patent Laid-Open No. 2002-504800).
Electronic equipments such as cellular phones are equipped with functionalities other than a telephone, including a digital camera, a radio, a television, etc. In addition, recent cellular phones are equipped with a high-resolution display device for obtaining high-quality images, or a substitute display device or a flash for use with a camera. Enhancement of the above-mentioned cellular phone functionalities increases power consumption.
At the same time, considering the portability of cellular phones, the external size of cellular phones is required to be smaller and slimmer, which in turn requires batteries with a reduced volume. There is, thus, an increasing need for a smaller power apparatus which keeps the cellular phone operating over a long time period.
Now, in the Patent Literatures 1 and 2, batteries serving as the power apparatus are switched by monitoring (detecting) the voltage of the backup battery (internal battery) and the battery pack (external battery), respectively. However, power supply from the battery pack to the control circuit (battery switching circuit) stops when the battery pack is suddenly detached from the cellular phone during the use of the battery pack. Calls are thus forcibly terminated because the power apparatus of the cellular phone turns off before the power apparatus switches from the battery pack to the backup battery.
Here the Patent Literature 2 describes that software is designed to switch to the internal battery when the external battery is detached (see Paragraph “0027” of the Patent Literature 2). However, the patent literature 2 lacks disclosure of a concrete arrangement for switching from the external battery to the internal battery when the external battery is detached, hence preventing implementation as a product. In other words, the above-mentioned software design alone may not practically avoid turning off the power before switching from the external battery to the internal battery, when the external battery is detached.